I've got a really big file to render, and I've played with render layers. But then I wanted to put everything back like it was before, to render everything in one piece, but now I have a problem because when I render the final object, the render doesn't stop. It says Freestyle: Mesh loading 99% and no matter how long I leave it, it stays at 99% and after 15 minutes blender crashes. How to change that? I'm not sure how the render layers work right now, so I want to render everything at once like I did before.
When a render dies on Freestyle, it's usually a RAM issue. Freestyle takes a LOT of RAM (significantly more than Cycles for the same scene.) Once it runs out of your regular RAM, it will go into pagefile/virtual memory. This will slow your computer down to a crawl, because it's using your hard drive as memory. If it also runs out of pagefile space, it will crash. This is likely your issue.
The work around, if you were to attempt to still use freestyle, is to cut the scene down into more layers. Technically you can increase pagefile to give it more to work with, but even with a solid state drive this will be so slow as to be pointless.